The present invention relates to a liquid crystalline composition with improved adhesivity to tacky adhesives and adhesives, a liquid crystal film comprising such a composition, and a liquid crystal display device equipped with such a film.
In recent years, as a result of the researches and developments which have been actively conducted to apply liquid crystal materials for optical purposes, a liquid crystal film produced by aligning a liquid crystal material and forming the material into a film has been practically used for the purposes of compensating the color and widening the viewing angle, of a liquid crystal display device.
Various methods of forming a liquid crystal material into a film have been known. For example, there is a method in which a liquid crystal film is produced by forming a thin film of a liquid crystal material over a substrate with alignability and then heating the film to a temperature equal to or higher than the glass transition temperature “Tg” so as to align the liquid crystal molecules, followed by quenching the film so as to fix the aligned molecules (see Patent Document Nos. 1 and 2). Alternatively, methods are known in which a film is produced by introducing a cross-linkable group into a liquid crystalline composition and then forming a film thereof over a substrate with alignability, followed by heating the film to a temperature equal to or higher than the Tg to align the liquid crystal molecules and then cross-linking the film by irradiation of light to fix the liquid crystal molecules in the aligned state (see Patent Document Nos. 3 to 6).
These methods can produce aligned films fixed in a liquid crystal alignment state. These films have various structures such as those where a film is kept formed on a substrate (substrate/(alignment film)/aligned film) and those where an aligned film is transferred to a transparent film substrate different from the alignment substrate via a tacky adhesive or an adhesive (transparent film substrate/tacky adhesive or adhesive/alignment film) (see Patent Document Nos. 7 and 8). These aligned films are used in combination with a retardation film or a polarizer via a tacky adhesive or an adhesive, in a liquid crystal display device. As the result of widespread use of liquid crystal display devices, these combined films are required to have properties under severer environments specifically heat resistance under elevated temperature conditions and moisture resistance under elevated humidity conditions. Therefore, adhesivity between an aligned film and a tacky adhesive or an adhesive is strongly required to be high, and various modifications have been studied (see Patent Documents 9 and 10).
The same is applied to a tacky adhesive and an adhesive which are used to transfer an aligned film to a transparent substrate. If such an tacky adhesive or adhesive is insufficient in adhesivity to an aligned film, there would arise a disadvantage that the aligned film may not be sufficiently transferred to another film. Heretofore, there was no particular restriction on tacky adhesives or adhesives used for laminating or transferring as long as they are of optical grades. However, (meth)acrylic tacky adhesives and adhesives have been frequently used because they have wide variety of properties and are easy in handling. As described above, adhesivity between an aligned film formed of a liquid crystal compound and a (meth)acrylic tacky adhesive or adhesive has also been strongly required to be further improved due to the requirements regarding the aforesaid resistance to the environments, of liquid crystal display devices. It is assumed that addition of a (meth)acrylic compound into a film formed of a liquid crystal compound would enhance adhesivity to a (meth)acrylic tacky adhesive or adhesive. However, the influences of addition of the (meth)acrylic compound cause problems that defects in aligning of liquid crystal molecules would likely occur due to an extreme reduction in the alignability of the liquid crystalline composition and heat resistance or moisture resistance would be diminished.                (1) Patent Document No. 1: Japanese Patent Laid-Open Publication No. 3-9326        (2) Patent Document No. 2: Japanese Patent Laid-Open Publication No. 6-20434        (3) Patent Document No. 3: Japanese Patent Laid-Open Publication No. 9-73081        (4) Patent Document No. 4: Japanese Patent Laid-Open Publication No. 2002-146353        (5) Patent Document No. 5: Japanese Patent Laid-Open Publication No. 2002-308832        (6) Patent Document No. 6: Japanese Patent Laid-Open Publication No. 2003-139953        (7) Patent Document No. 7: Japanese Patent Laid-Open Publication No. 4-57017        (8) Patent Document No. 8: Japanese Patent Laid-Open Publication No. 8-278491        (9) Patent Document No. 9: Japanese Patent Laid-Open Publication No. 2000-321426        (10) Patent Document No. 10: Japanese Patent Laid-Open Publication No. 2001-49205        